1. Field of the Disclosure
The present invention relates to apparatus for compressing and expanding a gas, a method of operating the same, and particularly but not exclusively to energy storage apparatus including such apparatus for compressing and expanding a gas.
2. Description of the Related Art
Many energy storage processes involve operating gas compressors and/or expanders as part of the technology. For example, conventional energy storage techniques such as CAES (Compressed Air Energy Storage) and its variants use compressors and expanders to process gas, as does the novel energy storage technique disclosed in the applicant's own earlier application WO 2009/044139.
Certain rotary machinery has been designed to operate with gas flows in both directions, although the efficiency in each direction is normally quite low. However, most rotary machinery is normally configured to operate with gas flows passing in one direction only and hence it is necessary to have separate machinery for charge and discharge cycles.